Needle lift damper device of injector for fuel injection and needle lift damping method

ABSTRACT

An object of the present invention is to obtain a consistently stable needle lift damping effect in an injector  8   b  for fuel injection. In an injector  8   b  that relieves fuel pressure inside a pressure control chamber  37  and lifts a needle valve  36,  there are provided a damper member  62  that is slidably mounted to the needle valve  36,  a damping chamber  63  formed between the damper member  62  and the needle valve  36,  a leak passage  64  for extracting and leaking out the fuel in the damping chamber  63,  and a stopper member  41  to restrict the lift position of the damper member  62.  Damping of the lift of the needle valve  36  is carried out by extracting and leaking out the fuel in the damping chamber  63  through the leak passage  64.  The needle valve  36  functions as a guide for the damper member  62,  and prevents vibration of the damper member  62,  allowing a consistently stable damping effect to be obtained.

REFERENCE TO PRIOR APPLICATION

This application is entitled to the benefit of and incorporates byreference essential subject matter disclosed in PCT Patent ApplicationNo. PCT/JP00/08137 filed on 17 Nov. 2000.

TECHNICAL FIELD

The present invention relates to a needle lift damper device in aninjector for fuel injection, and a needle lift damping method. Inparticular, it relates to a device and method for damping needle valvelift in order to decrease the initial injection rate of a common railinjector in a diesel engine.

BACKGROUND ART

FIG. 4 shows an outline of a common rail-type fuel injection device in adiesel engine. As shown in the drawing, in this device, fuel within afuel tank 1 is supplied to a high-pressure pump 4 through a filter 2 anda feed pump 3. After being pressurized to a high pressure (tens tohundreds of MPa) by the high-pressure pump 4, the fuel goes through apassage 5 and is stored in an accumulator called a common rail 6. Thefuel inside the common rail 6 is supplied to each injector 8 through afuel supply passage 7.

As shown in FIG. 5, a portion of the high-pressure fuel that is suppliedto each injector 8 is supplied to a pressure control chamber 10 througha passage 9 and the remaining portion is supplied through a passage 11to a fuel puddle 13 at the tip of a needle valve 12. The fuel pressureinside the pressure control chamber 10 is maintained and released by arelief valve 14. The relief valve 14 is depressed by a conventionalspring 15 and closes a relief hole 16, maintaining the fuel pressure inthe pressure control chamber 10. When an electromagnetic solenoid 17 isdriven by an electric current, the relief valve 14 resists the spring 15and is lifted up, thereby opening the relief hole 16 and releasing thefuel pressure in the pressure control chamber 10. Further, the needlevalve 12 is constantly forced downwards by a spring 18.

In such injectors 8, when the electric current to the electromagneticsolenoid 17 is turned off, the relief hole 16 is closed by the reliefvalve 14 that is pressed down by the spring 15; and since the fuelpressure in the pressure control chamber 10 is maintained, the downwardforce on the needle valve 12 created by such fuel pressure and thespring 18 becomes greater than the upward force thereon created by thefuel pressure in the pressure-receiving portion 19 at the tip (fuelpuddle 13) of the needle valve 12; and accordingly the needle valve 12moves downward. Consequently, a conical portion 20 at the tip of theneedle valve 12 is mounted to a seat 21, closing a spray hole 22 of theinjector 8 so that fuel injection does not occur. thereon created by thefuel pressure in the pressure-receiving portion 19 at the tip (fuelpuddle 13) of the needle valve 12; and accordingly the needle valve 12moves downward. Consequently, a conical portion 20 at the tip of theneedle valve 12 is mounted to a seat 21, closing a spray hole 22 of theinjector 8 so that fuel injection does not occur.

Further, when the electromagnetic solenoid 17 is driven by an electriccurrent, the relief valve 14 resists the spring 15 and is lifted up; andsince the relief hole 16 is opened and the fuel pressure in the pressurecontrol chamber 10 is released, the upward force on the needle valve 12created by the fuel pressure in the pressure receiving portion 19 at thetip (fuel puddle 13) of the needle valve 12 becomes greater than thedownward force thereon created by the fuel pressure and the spring 18;and accordingly the needle valve 12 lifts upward. Consequently, theconical portion 20 at the tip of the needle valve 12 becomes detachedfrom the seat 21 and high pressure fuel is injected from the spray hole22 of the injector 8. Note that the fuel flowing out of the pressurecontrol chamber 10 is returned to the fuel tank 1 through a fuel returnpassage 23 (See FIG. 4).

In the above-mentioned injector 8, it is desirable that the needle valve12 is made to lift upward comparatively smoothly (slowly). If the needlevalve 12 is made to lift upwards comparatively smoothly, the initialinjection rate of the fuel injected from the spray hole 22 decreases,and since the first ignition after an ignition delay occurs with a lowinjection rate and a small amount of fuel, a smooth first ignition canbe guaranteed, resulting in less NOx emitted and a decrease in noise.

FIG. 6 shows an injector that is known to lift the needle valve 12comparatively slowly (for example, Japanese Patent Application Laid-openNo. S59-165858). Note that since this injector 8 a has some constituentparts that are the same as the previously mentioned injector 8,identical reference numerals are used for the same constituent parts,and explanations are omitted. Only the different parts are explained.

In the injector 8 a shown in FIG. 6, a member 24 is attached to theupper end of the needle valve 12, and the pressure control chamber 10 isformed above the member 24. The relief hole 16 is formed on the ceilingof the pressure control chamber 10. A seat 25 that is in a raisedposition is formed around the relief hole 16. The relief hole 16 isopened and closed by the relief valve 14, having an orifice hole 26 inits center, when it mounts to and disengages from the seat 25.

The relief valve 14 is pressed onto the seat 25 by a conventional spring27, thereby closing the relief hole 16; and when fuel is supplied from athree-way valve 28, due to the fuel pressure, the relief valve 14resists the spring 27 and is pushed downward, opening the relief hole16. The three-way valve 28 is positioned in the passage 9 leading fromthe common rail 6 (see FIG. 4) to the pressure control chamber 10 and isswitched over as appropriate between a state where X-Y are linked toeach other and a state where Y-Z are linked to each other.

FIG. 6 shows the state when fuel injection has ceased. At this time, X-Yare linked to each other, the relief valve 14 is mounted to the seat 25,and the downward force on the needle valve 12 created by the fuelpressure inside the pressure control chamber 10 and the spring 18 isgreater than the upward force thereon created by the fuel pressure inthe fuel receiving portion 19 at the tip (fuel puddle 13) of the needlevalve 12. Consequently, the needle valve 12 moves downward and theconical portion 20 is mounted to the seat 21, closing the spray hole 22so that fuel injection does not occur. From this state, when thethree-way valve 28 operates so that Y-Z are linked to each other, sincethe fuel in the pressure control chamber 10 is gradually squeezed fromthe orifice hole 26 in the relief valve 14 and flows out, the fuelpressure in the pressure control chamber 10 decreases at a smooth paceand the needle valve 12 lifts upward comparatively slowly. In this waylift damping of the needle valve is achieved and the initial injectionrate from the spray hole 22 is decreased.

Subsequently, when the three-way valve 28 operates so that X-Y arelinked to each other for a second time, since the fuel in the commonrail 6 flows through passages 7 and 9 in a high-pressure state into thepressure control chamber 10, the relief valve 14 resists the spring 27and is depressed due to the fuel pressure. The fuel flows into thepressure control chamber 10 in one burst and the fuel pressure in thepressure control chamber 10 rises at once, so the needle valve 12 movesdownward rapidly. Consequently, the injection cut-off of the fuelinjected from the spray hole 22 is improved.

However, in the above-mentioned injector 8 a, since damping the lift ofthe needle valve 12 is achieved by mounting the relief valve 14 to theseat 25 as well as making the fuel in the pressure control chamber 10leak out while being squeezed from the orifice hole 26, disturbance inthe leak flow that occurs at the time of leakage from the orifice hole26 can cause the relief valve 14 to vibrate and momentarily becomedislodged from the seat 25.

When this occurs, since the fuel in the pressure control chamber 10leaks not only from the orifice hole 26 but also from the gap betweenthe relief valve 14 and the seat 25, the damping effect in respect ofthe lift of the needle valve 12 becomes lower than the design value anda sufficient damping effect is not obtained. Further, such a problem isintermittent on each occasion of leakage from the orifice hole 26 (orinjection from the spray hole 22), thus making it difficult in fact toobtain a stable damping effect (initial injection rate reductioneffect).

More specifically, in the above-mentioned injector 8 a, the pressurecontrol chamber 10 that controls the upward and downward movement(opening and closing) of the needle valve 12 also functions as a dampingchamber for damping the needle valve 12. Therefore, in order to performdamping when the needle valve 12 is lifting upward, while it isnecessary that the relief valve 14 is mounted to the seat 25 and issealed, it is also necessary that the sealed portion (relief valve 14and seat 25) is disengaged when the needle valve 14 is moving downward.

In this way, since the sealed portion (relief valve 14 and seat 25) ismounted together and disengaged during the upward and downward movementof the needle valve 12, when the needle valve 12 is lifting upward, asdescribed above, the relief valve 14 vibrates and may momentarily becomedislodged from the seat 25 due to the pressure variation of the pressurecontrol chamber 10 that functions as a damping chamber, thereby makingthe seal defective.

It is an object of the present invention, which was designed with theforegoing circumstance in mind, to provide a needle lift damper devicein an injector for fuel injection and a needle lift damping method thatenables a stable damping effect to be consistently obtained.

A further object of the present invention is to provide a needle liftdamper device in an injector for fuel injection and a needle liftdamping method that enables a stable fuel leak to be consistentlyproduced.

A further object of the present invention is to provide a needle liftdamper device in an injector for fuel injection and a needle liftdamping method that enables the initial injection rate of each injectionto be stabilized.

DISCLOSURE OF INVENTION

The present invention is a damper device designed to achieve damping ofthe lift of a needle valve in an injector that lifts the needle valvethat is depressed after receiving fuel pressure inside the pressurecontrol chamber, by relieving the fuel pressure. It comprises a dampermember slidably mounted to the needle valve; a damping chamber thatbecomes filled with fuel, formed between the damper member and theneedle valve; a leak passage for extracting fuel from inside the dampingchamber and leaking it outside the chamber; and a stopper member locatedabove the damper member for restricting the lift position of the dampermember.

According to the present invention, since the damper member is slidablymounted to the needle valve, the needle valve guides the damper memberin an upward and downward movement and prevents vibration of the dampermember. In such a way, a stable damping effect can be consistentlyproduced.

It is desirable that the damper member is slidably inserted in an axialdirection into a hole formed in the needle valve.

The stopper member is positioned above the needle valve and the pressurecontrol chamber is defined therebetween, while the hole is formed to aprescribed depth axially from the upper surface of the needle valve, andthe damper member is inserted into this hole from above and is able tomove up and down in the pressure control chamber. The damping chamber isformed between the damper member and the hole, and it is desirable toform the leak passage passing through the damper member in an axialdirection.

The upper end of the damper member is a flange that is larger indiameter than the hole and smaller in diameter than the upper surface ofthe needle valve and it is desirable that this flange is positionedabove the hole and upper surface of the needle valve as well as beingpositioned inside the pressure control chamber.

It is desirable that a biasing means to impel the damper member upwardsis formed in the damping chamber.

The biasing means consists of a coil spring, and it is desirable that aspring insertion hole having a prescribed depth is formed in the dampermember facing upward from the bottom thereof, and that the coil springis inserted into this spring insertion hole.

It is desirable that a relief passage, opening into the pressure controlchamber to relieve the fuel pressure therein, is formed in the stoppermember.

It is desirable that when the damper member abuts against the stoppermember, the relief passage is prevented from communicating with thepressure control chamber and communicates with the damping chamberthrough the leak passage.

It is desirable that the fuel pressure is introduced into the pressurecontrol chamber through the relief passage.

It is desirable that above the stopper member, a relief valve to openand close the exit of the relief passage and an driving means to drivethe opening and closing of the relief valve are formed.

The driving means may consist of a spring and electromagnetic solenoid.

When the relief valve is closed and a prescribed period of time haselapsed, the pressure control chamber and the damping chamber reach ahigh pressure equal to the fuel pressure and the needle valve isdepressed. Fuel injection is halted and the damper member abutsagainststopper member. It is desirable that from this state, when therelief valve opens, the high-pressure fuel in the damping chamber flowsthrough the leak passage and is gradually leaked into the reliefpassage, enabling the needle valve to lift up comparatively smoothly sothat the initial injection is conducted comparatively smoothly. It isdesirable that from this state, when the relief valve is closed, thefuel pressure supplied to the relief passage acts on the damper membersuch that the damper member and the needle valve are depressed together,making the needle valve move downward comparatively rapidly and haltingthe fuel injection comparatively rapidly.

When applied to a common rail-type fuel injection device in a dieselengine, the fuel pressure can be supplied from the common rail.

The present invention is also a method for damping the lift of theneedle valve in an injector that lifts the needle valve that isdepressed after receiving fuel pressure in the pressure control chamber,by relieving the fuel pressure. A damper member is slidably mounted tothe needle valve; a damping chamber that becomes filled with fuel isformed therebetween; a leak passage for extracting fuel from inside thedamping chamber and leaking it outside the chamber is formed; and astopper member positioned above the damper member for restricting thelift position thereof is formed. When the needle valve lifts, the fuelin the damping chamber is extracted and leaked through the leak passage,thereby damping the lift of the needle valve.

It is desirable that the damper member is slidably inserted in an axialdirection into a hole formed in the needle valve.

The stopper member is positioned above the needle valve and the pressurecontrol chamber is defined therebetween, while the hole is formed to aprescribed depth from the upper surface of the needle valve in an axialdirection, and the damper member is inserted into this hole from aboveand is able to move up and down in the pressure control chamber.

The damping chamber is formed between the damper member and the hole,and it is desirable to form the leak passage so as to pass through thedamper member in an axial direction. It is desirable that the dampermember is impelled upward by a biasing means formed in the dampingchamber.

It is desirable that a relief passage, opening into the pressure controlchamber is formed axially so as to pass through the stopper member, andthe fuel pressure in the pressure control chamber is relieved by thisrelief passage.

The relief passage and leak passage are positioned on the same axis andwhen the damper member abuts against the stopper member, the reliefpassage is prevented from communicating with the pressure controlchamber, but instead communicates with the damping chamber through theleak passage; and it is desirable that before the needle valve begins tolift, the damper member is made abut against the stopper member.

When the relief valve is closed and a prescribed period of time haselapsed, the pressure control chamber and the damping chamber reach ahigh pressure equal to the fuel pressure, and the needle valve isdepressed. Fuel injection is halted and the damper member abuts againstthe stopper member.

It is desirable that from this state, when the relief valve opens, thehigh-pressure fuel in the damping chamber flows through the leak passageand is gradually leaked into the relief passage, enabling the needlevalve to lift up comparatively smoothly, with the result that theinitial injection is carried out comparatively smoothly.

It is desirable that from this state, when the relief valve is closed,the fuel pressure supplied to the relief passage acts on the dampermember so that the damper member and the needle valve are depressedtogether, making the needle valve move downward comparatively rapidlywith the result that fuel injection is halted comparatively rapidly.

When applied to a common rail-type fuel injection device in a dieselengine, the fuel pressure can be supplied from the common rail.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a longitudinal sectional view showing an injector according toa preferred embodiment of the present invention and showing the fuelinjection standby mode;

FIG. 2 is a longitudinal sectional view showing an injector according toa preferred embodiment of the present invention and showing the fuelinjection mode;

FIG. 3 is a longitudinal sectional view showing an injector according toa preferred embodiment of the present invention and showing thefuel_injection completion mode;

FIG. 4 is a compositional view showing a common rail-type fuel injectiondevice;

FIG. 5 is a longitudinal sectional view showing a conventional injectorfor fuel injection; and

FIG. 6 is a longitudinal sectional view showing a conventional injectorfor fuel injection equipped with a needle lift damper device.

BEST MODE FOR CARRYING OUT THE INVENTION

Preferred embodiments of the present invention will be described below,based on the attached drawings.

FIG. 1 shows an injector according to the present embodiment. Theinjector 8 b is applied in the aforementioned common rail-type fuelinjection device shown in FIG. 4, and has a nozzle body 30 wherein afuel supply passage 7 and a fuel return passage 23 are connected. Thenozzle body 30 is formed in a cylindrical state and a needle valve 36 isslidably contained axially therein, able to move up and down on the sameaxis. Further, inside the nozzle body 30, a stopper member 41 isinserted and fixed above the needle valve 36, separated therefrom at aprescribed distance.

Between the needle valve 36 and the stopper member 41, a pressurecontrol chamber 37 is defined and formed. The pressure control chamber37 is defined by an upper surface 38 of the needle valve 36, an insidesurface 40 of the nozzle body 30, a lower surface 42 of the stoppermember 41 and a damper member 62 that will be described later. In thecentral portion of the stopper member 41, a relief passage 45 to relievethe fuel pressure (fuel) in the pressure control chamber 37 upward, isformed to pass through the stopper member 41 in an axial direction. Theupper surface of the stopper member 41 is depressed in a tapered stateso that its center is as low as possible, and the exit of the reliefpassage 45 opens into the center of the upper surface. The rim of thisopening is the seat 48 of the relief valve 47 that opens and closes therelief passage 45. The lower surface 42 of the stopper member 41 is aflat surface perpendicular to the axial direction and the entry of therelief passage 45 opens into it.

The relief valve 47 is positioned above the stopper member 41 and opensand closes the exit of the relief passage from above. Further, a spring49 and an electromagnetic solenoid 50 are located above the relief valve47. The spring 49 forces the relief valve 47 downward and theelectromagnetic solenoid 50 is provided with an electric current from anexternal control unit to drive it and is turned ON and OFF. Note thatthe electromagnetic solenoid 50 also acts as the stopper that blocks thetop release portion of the nozzle body 30. When the electromagneticsolenoid 50 is turned to OFF (not conducting), the relief valve 47 isdepressed by the spring 49 and is mounted to the seat 48 so that therelief passage 45 closes. When the electromagnetic solenoid 50 is turnedto ON (conducting), due to the electromagnetic force, the relief valve47 acts against the force of the spring 49 and is pulled upward. Itdetaches from the seat 48 and opens the relief passage 45. The upper endof the relief valve 47 is shaped like a disc and is the part thatreceives the spring 49. The bottom is spherical and is the part wherethe seat 48 is mounted.

The electromagnetic solenoid 50 is located above the stopper member 41,separated at a prescribed distance; and between the electromagneticsolenoid 50 and the stopper member 41 a relief chamber 52 is formed toretain for a time the fuel that flows out of the pressure controlchamber 37 through the relief passage 45. The relief chamber 52 links tothe fuel return passage 23, and the fuel in the relief chamber 52 isreturned to a fuel tank 1 through the fuel return passage 23.

The approximate upper half of the needle valve 36 rubs against theinside surface 40 of the nozzle body 30, while the approximate lowerhalf is smaller in diameter than the inside surface 40, so that a fuelpuddle 31 forms between it and the nozzle body 30. The bottom (end) ofthe needle valve 36 and the nozzle body 30 fit together to form aconical shape, and the conical portion 58 of the bottom of the needlevalve 36 mounts to and becomes detached from a seat 57 at the bottom ofthe nozzle body 30, opening and closing a spray hole 59.

The fuel supply passage 7 branches out in the middle, and one branchpassage 7 a communicates with the relief passage 45 while the otherbranch passage 7 b communicates with the fuel puddle 31. Therefore, thehigh-pressure fuel (tens to hundreds of MPa) in the common rail 6 asshown in FIG. 4, is constantly supplied to the relief passage 45 throughthe fuel supply passage 7 and the one branch passage 7 a, and isconstantly supplied to the fuel puddle 31 through the fuel supplypassage 7 and the other branch passage 7 b.

Particularly, in this injector 8 b, a damper device to perform dampingon the upward movement (lift) of the needle valve 36 is formed. Thisdamper device mainly comprises a damper member 62 slidably mounted tothe needle valve 36; a damping chamber 63 that becomes filled with fuel,formed between the damper member 62 and the needle valve 36; a leakpassage 64 for extracting fuel from inside the damping chamber 63 andleaking it outside the chamber; and a stopper member 41 positioned abovethe damper member 62 for restricting the lift position of the dampermember 62.

The damper member 62 is a hollow cylindrical shape and is slidablyinserted from above in an axial direction into a hole 66 of thecross-sectional circle formed in the needle valve 36, on the same axis.It is positioned inside the pressure control chamber 37 and is able tomove up and down therein. The hole 66 is formed in the central portionof the needle valve 36 and is formed to a prescribed depth in an axialdirection from the upper surface 38 of the needle valve 36. It has afixed inside diameter along its whole depth. The damper member 62combines a flange 67 at its upper end and a cylinder 68 extending frombelow the flange 67. The cylinder 68 has about the same diameter as thehole 66 and is slidably inserted into the hole 66. However, thecircumference at the upper end of the cylinder 68 is narrowed so thatits diameter is smaller and a small gap 69 is formed between it and theinner surface of the hole 66. The flange 67 is bigger in diameter thanthe hole 66 and is smaller in diameter than the upper surface 38 of theneedle valve and the inside surface 40 of the nozzle body, and ispositioned so as to protrude above the hole 66 and the upper surface 38of the needle valve, while also being positioned in the pressure controlchamber 37.

In this way, a damping chamber 63 is formed between the damper member 62and the hole 66 of the needle valve 36. In the damping chamber 63, abiasing means is formed to impel the damper member 62 upward. Thebiasing means here consists of a coil spring 70 which is inserted in acompressed state into a spring insertion hole 71 consisting of thecentral hole of the cylinder 68, and is supported by the circumference,preventing bending and the like. The spring insertion hole 71 is formedfrom the bottom of the cylinder 68 upward to a prescribed depth, in thiscase so as to reach the flange 67.

The leak passage 64 is positioned in the center of the flange 67 on thesame axis as the relief passage 45, and is formed to pass through theflange 67 in an axial direction. The inside diameter is sufficientlysmall to be able to block the flow of fuel from the damping chamber 63,and is sufficiently small in comparison to the inside diameter of therelief passage 45.

As shown in FIG. 1, when the damper member 62 lifts upward the flange 67abuts against the stopper member 41 and the lift position is restricted.At this time the entire upper surface of the flange 67 has surfacecontact with and mounts to the lower surface 42 of the stopper member 41and in fact closes the relief passage 45. Accordingly, the reliefpassage 45 no longer communicates with the pressure control chamber 37,but instead communicates with the damping chamber 63 through the leakpassage 64.

Conversely, as shown in FIG. 3, when the damper member 62 is movingdownward and the flange 67 becomes detached from the stopper member 41,the relief passage 45 communicates with the pressure control chamber 37and also communicates with the damping chamber 63 through the leakpassage 64.

Next the application of this embodiment will be explained.

FIG. 1 shows the state when the electromagnetic solenoid 50 is OFF, inother words, after the relief valve 47 has closed and a prescribedperiod of time has elapsed. At this time, since the relief valve 47 hasclosed the relief passage 45, the relief passage 45, the pressurecontrol chamber 37, the leak passage 64 and the damping chamber 63 havean equal fuel pressure to that sent from the common rail 6. Accordingly,the downward force on the needle valve 36 created by this fuel pressureand the spring 55 becomes greater than the upward force thereon createdby the fuel pressure in the fuel puddle 31, and the needle valve 36 ispressed downward. Accordingly the conical portion 58 of the needle valve36 is mounted to the seat 57 and the spray hole 59 is closed, haltingfuel injection.

As described above, at this time the damper member 62 is pressed ontothe lower surface 42 of the stopper member 41 by the coil spring 70, andthe relief passage 45 communicates only with the damping chamber,through the leak passage 64.

From this state, when the electromagnetic solenoid 50 is ON, in otherwords when the relief valve 47 is opened, as shown in FIG. 2, the reliefvalve 47 is pulled upward and the relief passage 45 is opened, therebydischarging (leaking) fuel in the damping chamber 63 through the leakpassage 64 and relief passage 45. When this happens the fuel pressure inthe damping chamber 63 decreases, lessening the downward force on theneedle valve 36 accordingly. Consequently, the upward force on theneedle valve 36 becomes greater than the downward force thereon, and theneedle valve 36 lifts upward. Accordingly the conical portion 58 becomesdetached from the seat 57 and the high-pressure fuel stored in the fuelpuddle 31 is injected from the spray hole 59.

In particular, when the needle valve 36 lifts, the fuel in the dampingchamber 63 is discharged while being extracted in the leak passage 64.Therefore the high pressure in the damping chamber 63 is easier tomaintain and this high pressure resists the needle valve 36 that isattempting to lift. In other words, the needle valve 36 receivesresistance as it lifts. Consequently, the needle valve 36 liftscomparatively smoothly and at slow speed. Due to this, damping of thelift of the needle valve 36 is achieved and the initial injection rateis decreased.

From this state, when the electromagnetic solenoid 50 is OFF, in otherwords when the relief valve 47 is closed, first the fuel pressuresupplied to the relief passage 45 acts directly in a downward directionon the upper surface of the flange 67 of the damper member 62. When thishappens the damper member 62 moves downward slightly and detaches fromthe stopper member 41. At this instant the high-pressure fuel flows allat once from the gap into the pressure control chamber 37. Accordingly,the damper member 62 and the needle valve 36 are pressed downwardtogether by this high-pressure fuel. Meanwhile, the pressure hasdecreased at the tip of the needle valve 36 since the fuel has flowedfrom the spray hole 59. Consequently, the downward force on the needlevalve 36 suddenly becomes greater than the upward force thereon, and asshown in FIG. 3, the needle valve 36 moves downward comparativelyrapidly, and the conical portion 58 is mounted to the seat 57 makingfuel injection halt comparatively rapidly. In this way, the injectioncut-off at the completion of injection is improved. FIG. 3 shows thestate immediately after the conical portion 58 has mounted and injectionhas ended.

After this, during the initial period, the pressure in the dampingchamber 63 is lower than the pressure in the pressure control chamber37. However, since the fuel in the pressure control chamber 37 isgradually supplied into the damping chamber 63 through the leak passage64 and a gap in the fitting in the damper member insertion part (to bedescribed later), the pressure in the damping chamber 63 increases andthe damper member 62 lifts upward relative to the needle valve 36because of this pressure and the coil spring 70. Finally there is areturn to the state shown in FIG. 1. In other words, once the reliefvalve 47 is closed and a fixed period of time has elapsed, the injectionstand-by mode in FIG. 1 is reached and for each injection the cycle ofFIG. 1_FIG. 2_FIG. 3_FIG. 1 is repeated.

In this embodiment, since the damper member 62 is slidably mounted tothe needle valve 36, the needle valve 36 functions as a guide for thedamper member 62, and the upward and downward movement of the dampermember 62 is stabilized. Particularly at the time of fuel injection asshown in FIG. 2, the damper member 62 does not vibrate. Accordingly, thefuel leakage can be stably produced and the needle valve 36 can belifted at a consistently stable speed. Thus the initial injection ratefor each injection can be stabilized. Further, since the damper member62 has a flange 67 and this flange 67 mounts to the stopper member 41with a comparatively wide area, this can also prevent vibration of thedamper member 62 and assists stabilization of injection.

In this case, a gap in the fitting is formed in the insertion partbetween the damper member 62 and the hole 66. Accordingly, at the timeof fuel injection, as shown in FIG. 2, the fuel in the pressure controlchamber 37 flows through this gap into the damping chamber 63. Ofcourse, the passage area of this gap is smaller than the area of theleak passage 64, so the leak speed of the fuel and the lift speed of theneedle valve 36 are restricted solely by the passage area of the leakpassage 64. Note that at this time the high-pressure fuel supplied tothe relief passage 45 continues to flow upward and is discharged.

Further, at the time of fuel injection, despite the lift speed of theneedle valve 36 being restrained from start to finish, if the passagearea between the conical portion 58 and the seat 57 is greater than thetotal area of the spray hole 59, injection can be carried out as usual.Since the total area of the spray hole 59 is exceptionally small, thisenables a shift to ordinary injection after a minimal amount of timefollowing the start of injection. In such a way, the present device isonly designed to substantially restrict the initial injection rate anddoes not affect fuel injection thereafter.

At the same time, the present embodiment is not of the same type as theconventional technology (FIG. 6), in which a pressure control chamber 10functions also as a damping chamber, but consists instead of the dampingchamber 63 that is separate from the pressure control chamber 37.Consequently, the increase and decrease of the pressure in the pressurecontrol chamber 37 and the damping chamber 63 can be producedindependently and stably, with the result that damping does not becomeerratic due to pressure variation in the pressure control chamber 37,and a stable damping effect can consistently be obtained.

Note that the embodiments of the present invention are not limited towhat has been described above. For example the shape and otherproperties of the needle valve and damping member may be changed. Asregards the driving means to open and close the relief valve, instead ofthe mechanism using electromagnetic force and the force of a springdescribed above, a mechanism for positive driving using fuel pressure,hydraulic pressure or air pressure for example may also be considered.Similarly, it is possible to use something other than a coil spring forthe biasing means to impel the damper member. Further, the presentinvention can be applied to a broad range of fuel injection devices, forexample, it can also be applied to an injector in a gasoline engine.

The present invention can be applied to a fuel injection device in anengine, particularly a common rail-type fuel injection device in adiesel engine.

What is claimed is:
 1. A needle lift damper device in an injector forfuel injection, which is a damper device provided, to produce damping ofthe lift of a needle valve, in an injector that lifts said needle valvethat is pressed downward under a fuel pressure inside a pressure controlchamber, by relieving said fuel pressure, comprising: a damper memberslidably mounted to said needle valve; a damping chamber that is formedbetween said damper member and said needle valve, and becomes filledwith fuel; a leak passage for extracting fuel from inside said dampingchamber and leaking it outside said chamber; and a stopper memberlocated above said damper member for restricting the lift position ofsaid damper member; wherein said damper member is inserted into a holeformed in said needle valve such that the damper member is slidable inan axial direction.
 2. The needle lift damper device in an injector forfuel injection according to claim 1, wherein said stopper member ispositioned above said needle valve, said pressure control chamber isdefined therebetween, while said hole is formed axially to have aprescribed depth from the upper surface of said needle valve, saiddamper member is inserted into said hole from above and is able to moveup and down in said pressure control chamber, said damping chamber isformed between said damper member and said hole, and said leak passageis formed so as to pass through said damper member in an axialdirection.
 3. The needle lift damper device in an injector for fuelinjection according to claim 2, wherein the upper end of said dampermember is a flange that is larger in diameter than said hole and smallerin diameter than the upper surface of said needle valve, and said flangeis positioned above said hole and said upper surface of said needlevalve and inside said pressure control chamber.
 4. The needle liftdamper device in an injector for fuel injection according to any one ofclaim 1, wherein a biasing means to impel said damper member upward isformed in said damping chamber.
 5. The needle lift damper device in aninjector for fuel injection according to claim 4, wherein said biasingmeans consists of a coil spring, a spring insertion hole having aprescribed depth is formed in said damper member so as to extend upwardfrom the lower end thereof, and said coil spring is inserted into saidspring insertion hole.
 6. The needle lift damper device in an injectorfor fuel injection according to any one of claim 1, wherein said stoppermember is provided with a relief passage, opening into said pressurecontrol chamber to relieve the fuel pressure therein.
 7. The needle liftdamper device in an injector for fuel injection according to claim 6,wherein, when said damper member abuts against said stopper member, saidrelief passage is prevented from communicating with said pressurecontrol chamber and communicates with said damping chamber through saidleak passage.
 8. The needle lift damper device in an injector for fuelinjection according to claim 6, wherein said fuel pressure is introducedinto said pressure control chamber through said relief passage.
 9. Theneedle lift damper device in an injector for fuel injection according toany one of claim 6, wherein above said stopper member, a relief valve toopen and close the exit of said relief passage and an driving means todrive the opening and closing of said relief valve are formed.
 10. Theneedle lift damper device in an injector for fuel injection according toclaim 9, wherein said driving means consists of a spring andelectromagnetic solenoid.
 11. The needle lift damper device in aninjector for fuel injection according to any one of claim 6, whereinwhen said relief valve is closed and a prescribed period of time haselapsed, said pressure control chamber and said damping chamber reach ahigh pressure equal to said fuel pressure and said needle valve isdepressed, fuel injection is halted, and said damper member abutsagainst said stopper member; from this state, when said relief valveopens, said high-pressure fuel in said damping chamber flows throughsaid leak passage and is gradually leaked into said relief passage,enabling said needle valve to lift up comparatively smoothly and saidinitial injection is carried out comparatively smoothly; from thisstate, when said relief valve is closed, said fuel pressure supplied tosaid relief passage acts on said damper member and said damper memberand said needle valve are depressed together, making said needle valvemove downward comparatively rapidly and fuel injection is haltedcomparatively rapidly.
 12. The needle lift damper device in an injectorfor fuel injection according to any one of claim 1, wherein when appliedto a common rail-type fuel injection device in a diesel engine, saidfuel pressure is supplied from said common rail.
 13. A needle liftdamping method in an injector for fuel injection, which is a dampingmethod for damping the lift of a needle valve in an injector that liftssaid needle valve that is depressed under a fuel pressure inside apressure control chamber, by relieving said fuel pressure, comprisingthe steps of: slidably mounting a damper member to said needle valve;forming a damping chamber that becomes filled with fuel, between saiddamper member and said needle valve; providing a leak passage forextracting fuel inside the damping chamber and leaking it outside thechamber; providing a stopper member positioned above said damper memberthat restricts the lift position thereof; and damping the lift of saidneedle valve by extra and leaking the fuel in said damping chamberthrough said leak passage when said needle valve is lifted; wherein saiddamper member is inserted into a hole formed in said needle valve so asto be slidable in an axial direction.
 14. The needle lift damping methodin an injector for fuel injection according to claim 13, wherein saidstopper member is positioned above said needle valve and said pressurecontrol chamber is defined therebetween, while said hole is formed to aprescribed depth axially from the upper surface of said needle valve;said damper member is inserted into said hole from above and is able tomove up and down in said pressure control chamber; said damping chamberis formed between said damper member and said hole; said leak passage isformed so as to pass through said damper member in an axial direction;and said damper member is impelled upward by a biasing means formed insaid damping chamber.
 15. The needle lift damping method in an injectorfor fuel injection according to any one of claim 13, wherein a reliefpassage, opening into said pressure control chamber is formed so as topass through said stopper member in an axial direction, and the fuelpressure in said pressure control chamber is relieved by said reliefpassage.
 16. The needle lift damping method in an injector for fuelinjection according to claim 15, wherein said relief passage and saidleak passage are positioned on the same axis and when said damper memberabuts against said stopper member, said relief passage is prevented fromcommunicating with said pressure control chamber and communicates withsaid damping chamber through said leak passage, and before said needlevalve begins to lift, said damper member is made abut against saidstopper member.
 17. The needle lift damping method in an injector forfuel injection according to claim 15, wherein, when said relief valve isclosed and a prescribed period of time has elapsed, said pressurecontrol chamber and said damping chamber reach a high pressure equal tothe fuel pressure and said needle valve is depressed, fuel injection ishalted and said damper member abuts against said stopper member; whensaid relief valve opens, from this state, said high-pressure fuel insaid damping chamber flows through said leak passage and is graduallyleaked into said relief passage, enabling said needle valve to lift upcomparatively smoothly and said initial injection is carried outcomparatively smoothly; and when said relief valve is closed, from thisstate, said fuel pressure supplied to said relief passage acts on saiddamper member and said damper member and said needle valve are depressedtogether, making said needle valve move downward comparatively rapidlyand fuel injection is halted comparatively rapidly.
 18. The needle liftdamping method in an injector for fuel injection according to any one ofclaim 13, wherein when applied to a common rail-type fuel injectiondevice in a diesel engine, said fuel pressure can be supplied from saidcommon rail.